The invention relates to a process for winning an electropositive metal from a metal carbonate, and also an arrangement for carrying out the process.
The proportion of carbon dioxide in the atmosphere has been increasing since the beginning of the 19th century because of industrialization. Carbon dioxide is a greenhouse gas. The Kyoto protocol defined reduction targets for proportions of greenhouse gases in the atmosphere in order to protect the climate. These reduction targets should be achieved by various climate protection measures. Firstly, a reduction in the emission of greenhouse gases, in particular of carbon dioxide, is necessary. This can, for example, be achieved by efficiency improvements in power generation. Furthermore, utilization of carbon dioxide as a material to produce basic chemicals or in combustion to produce energy (e.g. combustion in CO2) is useful.
WO 2012/038330 discloses a process in which carbon dioxide is converted into basic chemicals. Here, carbon dioxide which has been isolated beforehand from an offgas stream is burnt using an electropositive metal. The combustion forms basic chemicals such as carbon monoxide or carbides, which can, for example, be converted by hydrolysis into acetylene. Carbon monoxide can later be reacted further with hydrogen to form methanol or other products of value (Fischer-Tropsch process). The thermal energy liberated in the combustion of the electropositive metal in carbon dioxide, or alternatively in nitrogen, can be utilized, for example, for steam generation in order to drive generators or heat separation processes. After the combustion, the metal is often present in its lowest-energy form, viz. the metal carbonate. For a circular process based on the metal to be possible, the metal carbonate has to be recycled back to the metal. This is at present effected by first converting the metal carbonate into metal chloride. Here, the metal carbonate is dissolved in aqueous hydrochloric acid solution. The metal carbonate then reacts with the aqueous hydrochloric acid to form metal chloride. The aqueous metal chloride solution is subsequently heated in order to evaporate the water and produce anhydrous metal chloride. The evaporation of water consumes large quantities of energy (www.derneueschwan.ch/chemieberatung/question.php?q=14), which is disadvantageous.